Ans given below
-3r-12=-21
-3r=-21+12
-3r=-9
r=-9\-3
r=3
₇P₅ is a permutation. you can find this setting in the statistics menu of your scientific calculator (i think).
If you don't have a scientific calculator, you can use the following formula:
nPr = 
₇P₅ = 
= 
= 
= 7 * 6 * 5 * 4 * 3
= 2520
Answer: C
You could say that a(n) = 12 - 5n .
Then ...
a(1) = 12 - 5 = 7
a(2) = 12 - 10 = 2
a(3) = 12 - 15 = -3
and so on.
So it seems to work.
the 2 numbers are 8 and 40
40*2 = 80 +8 = 88